Cobalt and nickel complexes bearing pyrazolyliminophosphorane ligands: Synthesis, characterisation and catalytic ethylene oligomerisation behaviour

Article abstract of DOI:10.1002/ejic.200600651

Treatment of 1-(2′-azidophenyl)-3,5-dimethylpyrazole (1) with Ph ₂PR (R = Ph, Me) and (Ph₂P)₂CH₂, respectively, affords the pyrazolyliminophosphoranes 2, 3 and 4. Reaction of 2 or 3 with [NiCl₂(dme)] or NiBr₂ yields the N,N-chelate nickel complexes 5-8, and with CoCl₂ complexes 9 and 10. Reaction of 4 with [NiCl₂(dme)], NiBr₂ and CoCl₂, respectively, affords the N,N,P-chelate complexes 11-13. Compounds 2-4 were characterised by ¹H, ¹³C, ³¹P NMR and IR spectroscopy and elemental analysis, while complexes 5-13 were characterised by IR spectroscopy and elemental analysis. The structures of complexes 5, 9 and 12 were further characterised by single-crystal X-ray diffraction techniques. Complexes 5-13 are active catalysts for ethylene oligomerisation upon activation with alkylaluminium derivatives (Et₂AlCl, MAO or MMAO). These complexes exhibit good to high catalytic activities (up to 3.54 × 10 ⁶ g mol^-1 h atm for the nickel complexes and 5.48 × 10⁵ gmol^-1 h atm for the cobalt complexes). The effects of varying ethylene pressure, temperature and aluminium co-catalyst/Ni or Co ratios with complexes 5, 9, 11 and 12 are reported. Wiley-VCH Verlag GmbH & Co. KGaA, 2006.

Full text of DOI:10.1002/ejic.200600651

FULL PAPER
DOI: 10.1002/ejic.200600651
Cobalt and Nickel Complexes Bearing Pyrazolyliminophosphorane Ligands:
Synthesis, Characterisation and Catalytic Ethylene Oligomerisation Behaviour
Cheng Zhang,[a] Wen-Hua Sun,[b] and Zhong-Xia Wang*[a]
Keywords: Cobalt / Nickel / Homogeneous catalysis / Ethylene / Oligomerisation
Treatment of 1-(2Ј-azidophenyl)-3,5-dimethylpyrazole (1)
with Ph2PR (R = Ph, Me) and (Ph2P)2CH2, respectively, af-
fords the pyrazolyliminophosphoranes 2, 3 and 4. Reaction of
2 or 3 with [NiCl2(dme)] or NiBr2 yields the N,N-chelate
nickel complexes 5–8, and with CoCl2 complexes 9 and 10.
Reaction of 4 with [NiCl2(dme)], NiBr2 and CoCl2, respec-
characterised by single-crystal X-ray diffraction techniques.
Complexes 5–13 are active catalysts for ethylene oligomeri-
sation upon activation with alkylaluminium derivatives
(Et2AlCl, MAO or MMAO). These complexes exhibit good to
high catalytic activities (up to 3.54×106 gmol–1 hatm for the
nickel complexes and 5.48×105 gmol–1 hatm for the cobalt
tively, affords the N,N,P-chelate complexes 11–13. Com- complexes). The effects of varying ethylene pressure, tem-
pounds 2–4 were characterised by 1H, 13C, 31P NMR and IR
spectroscopy and elemental analysis, while complexes 5–13
were characterised by IR spectroscopy and elemental analy-
sis. The structures of complexes 5, 9 and 12 were further
perature and aluminium co-catalyst/Ni or Co ratios with
complexes 5, 9, 11 and 12 are reported.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2006)
gands that combine pyrazolyl and iminophosphorane units
for late transition metals relevant for catalysis of ethylene
polymerisation or oligomerisation. Herein we report the
synthesis, characterisation and catalytic performance for
ethylene oligomerisation of cobalt and nickel complexes
bearing pyrazolyliminophosphorane ligands.
Introduction
Ethylene oligomerisation to form linear α-olefins has be-
come a topic of considerable interest in both academia and
industry as these oligomers are used as co-monomers with
ethylene and for the preparation of a variety of important
compounds such as detergents, synthetic lubricants, addi-
tives for high-density polyethylene production and surfac-
tants.[1] Late transition metal complexes have demonstrated
potential as catalysts for ethylene oligomerisation. A repre-
sentative example is the nickel catalysts in the Shell higher
olefin process (SHOP).[2] Other late transition metal com-
plexes have also proved to be active. These complexes are
supported by extensive didentate and tridentate ligands, in-
cluding N,N,[3] N,P,[1,4] N,O,[5] P,O,[6] P,P,[7] N,N,P,[8]
N,N,N,[1b,3b,9] N,P,N[10] and P,N,P[11] ligands. Recently, che-
lating nitrogen ligands featuring iminophosphorane moie-
ties have attracted considerable attention. Examples include
I–V (Scheme 1).[3a–3d,12] Some of the late transition metal
complexes with these ligands exhibit ethylene polymerisa-
tion or oligomerisation activities in the presence of appro-
priate co-catalysts. Pyrazole-based ligands have also re-
ceived extensive attention in recent years for the preparation
of olefin polymerisation catalysts, including poly(pyrazol-
yl)borates, didentate bis-pyrazolyl ligands and mixed donor
ligands.[1b,4f,9b,13] Our aim was to examine a set of new li-
Scheme 1.
Results and Discussion
Synthesis and Characterisation of Compounds 2–13
Compound 1 was prepared according to a literature
method.[4f,14] Syntheses of ligands 2–4 and cobalt and
nickel complexes 5–13 are summarised in Scheme 2. Treat-
ment of 1 with one equivalent of phosphane Ph2PR (R =
Ph or Me) or Ph2PCH2PPh2 yielded iminophosphoranes 2–
4 in high yields. Reaction of 2 or 3 with MX2 (M = Ni, X
[a] Department of Chemistry, University of Science and Technol-
ogy of China,
Hefei, Anhui 230026, P. R. China
[b] Key Laboratory of Engineering Plastics, Institute of Chemistry,
The Chinese Academy of Sciences,
Beijing 100080, P. R. China
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C. Zhang, W.-H. Sun, Z.-X. Wang
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= Br; M = Co, X = Cl) or [NiCl2(dme)] afforded complexes of compounds.[3c,15] The P–N distance of 1.624(6) Å is nor-
5–10 in good to excellent yields. A similar reaction between mal for metal-coordinated iminophosphoranes.[3b,16]
4 and the metal halides gave complexes 11–13. Compounds
2–4 are yellow (2 and 4) or orange (3) solids and were fully
1
characterised by H, 13C and 31P NMR spectroscopy and
elemental analyses. Complexes 5–13 are blue (5–10 and 13),
purple (11) or yellow (12) crystals or powder. Complexes 5
and 7–13 are air stable and complex 6 forms an H2O adduct
after being exposed to air for a long period. These com-
plexes are paramagnetic and were characterised by IR spec-
troscopy and elemental analyses, as well as by single-crystal
X-ray diffraction techniques (for 5, 9 and 12).
Figure 1. ORTEP drawing of complex 5 (thermal ellipsoids at 30%
probability). Selected bond lengths [Å] and angles [°]: Ni(1)–N(1)
2.002(6), Ni(1)–N(3) 2.007(6), Ni(1)–Br(1) 2.3614(13), Ni(1)–Br(2)
2.3743(13), P(1)–N(1) 1.624(6), N(1)–C(19) 1.421(9), N(2)–N(3)
1.388(8), N(2)–C(24) 1.434(9), C(19)–C(24) 1.412(10); N(1)–Ni(1)–
N(3) 92.2(2), N(1)–Ni(1)–Br(1) 104.75(17), N(3)–Ni(1)–Br(1)
108.5(2),
N(1)–Ni(1)–Br(2)
113.81(16),
N(3)–Ni(1)–Br(2)
106.71(18), Br(1)–Ni(1)–Br(2) 125.71(6), C(19)–N(1)–Ni(1)
113.3(4), P(1)–N(1)–Ni(1) 124.4(3), C(27)–N(3)–Ni(1) 127.4(5),
N(2)–N(3)–Ni(1) 118.3(4), C(19)–N(1)–P(1) 121.5(5), N(3)–N(2)–
C(24) 119.1(6).
The structure of 9 is shown in Figure 2. Crystalline 9 is
monomeric and the Co centre is in a distorted tetrahedral
environment. Like complex 5, the six-membered metallacy-
cle also exists in a boat conformation in the solid state. The
Co–N distance (av. 2.045 Å) is close to that in
[{CH2(Ph2P=NPh)2}CoCl2] (av. 2.032 Å).[3b] The Co–Cl
Scheme 2. Synthesis of compounds 2–13. Reagents and conditions:
i) Ph2PR (R = Ph, Me), CH2Cl2, room temperature, 12 h; ii)
Ph2PCH2PPh2, CH2Cl2, room temperature, 12 h; iii) MX2 (M =
Ni, X = Br; M = Co, X = Cl) or [NiCl2(dme)], thf, room tempera-
ture, 15 h.
The structure of 5 is presented in Figure 1. Crystalline 5
is monomeric. Its Ni atom is four coordinate and has a
distorted tetrahedral geometry. The N1–C19–C24–N2
atoms lie in the same plane. The N1–Ni1–N3–N2 atoms are
also approximately co-planar, with a torsion angle of 4°.
The six-membered metallacycle shows a boat conformation.
The Ni1–N1 distance of 2.002(6) Å is longer than those
Figure 2. ORTEP drawing of complex 9 (thermal ellipsoids at 30%
probability). Selected bond lengths [Å] and angles [°]: Co(1)–N(2)
2.052(2), Co(1)–N(3) 2.038(2), Co(1)–Cl(1) 2.2376(10), Co(1)–Cl(2)
2.2476(10), P(1)–N(3) 1.610(2), N(1)–N(2) 1.385(3), N(1)–C(6)
1.435(4), C(1)–C(6) 1.401(4), N(3)–C(1) 1.427(3); N(3)–Co(1)–N(2)
91.54(9), N(3)–Co(1)–Cl(1) 108.60(7), N(2)–Co(1)–Cl(1) 113.27(8),
N(3)–Co(1)–Cl(2) 115.95(7), N(2)–Co(1)–Cl(2) 107.75(8), Cl(1)–
Co(1)–Cl(2) 117.01(4), N(1)–N(2)–Co(1) 117.84(18), C(1)–N(3)–
Co(1) 111.62(17), N(2)–N(1)–C(6) 119.4(2), C(1)–N(3)–P(1)
found
in
[{2-[Ph2P=N(C6H3Me2-2Ј,6Ј)]-6-(SiMe3)-
C5H3N}NiBr2] [1.996(8) Å] and [{2-(Ph3P=NCH2)-6-
MeC5H3N}NiBr2] [1.983(3) Å].[3c] The Ni1–N3 distance of
2.007(6) Å is close to that in [{1-(2Ј-Ph2PC6H4)-3,5-
Me2C3HN2}NiCl2] [2.003(4) Å],[4f] but slightly shorter than
those found in [{NH(1-CH2CH2-3,5-Me2-C3HN2)2}NiCl2]
[2.069(2) and 2.0334(19) Å, respectively].[1b] The two Ni–Br
122.10(18),
C(1)–N(3)–Co(1)
111.62(17),
P(1)–N(3)–Co(1)
bond lengths are very similar and are typical for this class 125.55(13).
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Co and Ni Complexes Bearing Pyrazolyliminophosphorane Ligands
FULL PAPER
distances [2.2376(10) and 2.2476(10) Å, respectively] are is slightly longer than that in complex 5 and comparable to
within the normal range for four-coordinate Co complex- those in [{NH(1-CH2CH2-3,5-Me2C3HN2)2}NiCl2]
es.[3b,3c,17] [2.069(2) and 2.0334(19) Å, respectively].[1b] Both P1 and P2
Single crystals of complex 12 suitable for X-ray crystal- exhibit distorted tetrahedral geometries. The Ni1–P1 dis-
lography were grown from toluene. The molecular structure tance of 2.4001(11) Å is longer than that in [{1-(2Ј-
of complex 12 is presented in Figure 3. Complex 12 is mo- Ph2PC6H4)-3,5-Me2C3HN2}NiCl2] [2.281(2) Å],[4f] but still
nomeric and co-crystallises with one toluene molecule. The within the normal range.[8]
coordination geometry around the nickel atom is distorted
trigonal bipyramidal in which the P1–Ni1–N3 angle is
167.57(9)° as a result of the strain imposed by the five- and
six-membered chelate rings. The N1–Ni1–Cl1–Cl2 atoms
Catalytic Properties of Complexes 5–13 for Ethylene
Oligomerisation
are nearly co-planar. The N1–C26–P2–Ni1 atoms are also
approximately in the same plane, the sum of the angles
around N1 being 359.92°. The Ni–N distance (av. 2.063 Å)
We initially examined the catalytic activities of complexes
5–10 using Et2AlCl as activator; the results are displayed in
Table 1. At an Al/metal molar ratio of 300 and 20 °C under
1 atm of ethylene the cobalt complexes 9 and 10 are inac-
tive, whereas complexes 5–8 catalyse the dimerisation and
trimerisation of ethylene with high activity (2.09×105 to
1.86×106 gmol–1 h; entries 3 and 11–13 in Table 1). The in-
fluence of the Al/Ni ratio, the reaction temperature and eth-
ylene pressure was investigated for complex 5. At 20 °C un-
der 1 atm of ethylene, when the ratio of Al to Ni was 300
complex
5
showed the highest catalytic activity
(1.34×106 gmol–1 hatm). Variation of the reaction tem-
perature also influences the catalytic activity and product
distribution. Thus, with a rise of the temperature from
20 °C to 40 °C and finally to 55 °C the catalytic activity of
5 gradually decreased and the proportion of C6 component
increased (entries 3, 7 and 8 in Table 1). At 0 °C the cata-
lytic activity of 5 was close to that at 40 °C. However, the
proportion of C6 component at 0 °C was far lower than
that at 40 °C (entry 3 in Table 1). This decrease of catalytic
Figure 3. ORTEP drawing of complex 12 (thermal ellipsoids at
30% probability). Selected bond lengths [Å] and angles [°]: Ni(1)– activity with a rise of temperature may be attributable to
N(1) 2.066(3), Ni(1)–N(3) 2.060(3), Ni(1)–Cl(2) 2.3012(11), Ni(1)–
the lower solubility of ethylene and the decomposition of
Cl(1) 2.3187(11), Ni(1)–P(1) 2.4001(11), P(2)–N(1) 1.603(3), P(1)–
the active sites at higher temperature. The catalytic activities
C(13) 1.842(3), P(2)–C(13) 1.806(3), N(2)–N(3) 1.377(4), N(2)–
of complexes 6 and 7 at 20 °C under 1 atm of ethylene and
C(31) 1.424(5), N(1)–C(26) 1.405(4), C(26)–C(31) 1.412(5); N(1)–
with
a
300:1 Al/Ni molar ratio (7.67×105 and
Ni(1)–N(3) 87.00(11), N(1)–Ni(1)–Cl(2) 129.22(9), N(3)–Ni(1)–
Cl(2) 92.76(9), N(1)–Ni(1)–Cl(1) 102.94(9), N(3)–Ni(1)–Cl(1)
94.35(9), Cl(2)–Ni(1)–Cl(1) 127.65(5), N(1)–Ni(1)–P(1) 80.64(8),
N(3)–Ni(1)–P(1) 167.57(9), Cl(2)–Ni(1)–P(1) 96,05(4), Cl(1)–Ni(1)–
P(1) 87.20(4), P(2)–N(1)–Ni(1) 118.82(15), C(26)–N(1)–Ni(1)
114.9(2), C(26)–N(1)–P(2) 126.2(2), N(2)–N(3)–Ni(1) 122.8(2),
C(13)–P(1)–Ni(1) 99.02(12), N(1)–P(2)–C(13) 106.93(15).
2.09×105 gmol–1 hatm, respectively) are lower than that of
complex 5. Complex 8 exhibits the highest catalytic activity
(1.86×106 gmol–1 hatm). Enhancement of the ethylene
pressure does not increase the catalytic activity of 5 in unit
pressure (entry 10 in Table 1). Comparison of the catalytic
Table 1. Ethylene oligomerisation with 5–8.[a]
Entry
Complex
Al/Ni
P [atm]
Time [h]
T [°C]
Activity[b]
C4 [%][c]
C6 [%][c]
1
2
3
4
5
6
7
8
5
5
5
5
5
5
5
5
5
5
6
7
8
50
1
1
1
1
1
1
1
1
1
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
1
0.5
0.5
0.5
0.5
20
20
20
20
20
0
40
55
20
20
20
20
20
2.24
7.99
13.4
7.30
7.09
5.50
5.64
2.86
14.3
71.3
7.67
2.09
18.6
67.3
82.1
78.8
73.4
54.1
74.0
13.3
5.4
76.9
79.2
64.7
77.8
72.1
32.7
17.9
21.2
26.6
45.9
26.0
86.7
94.6
23.1
20.8
35.3
22.2
27.9
200
300
400
600
300
300
300
300
300
300
300
300
9
10
11
12
13
10
1
1
1
[a] Conditions: 5 µmol of pre-catalyst, Et2AlCl as co-catalyst, 30 mL of toluene (120 mL of toluene with 10 atm of ethylene). [b]
105 gmol–1 h. [c] Weight percent determined by GC analysis.
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C. Zhang, W.-H. Sun, Z.-X. Wang
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Table 2. Ethylene oligomerisation with complexes 11 and 12.[a]
Entry
Complex
Al/Ni
P [atm]
Time [h]
t [°C]
Activity[b]
C4 [%][c]
C6 [%][c]
1
2
3
4
5
6
7
8
11
11
11
11
11
11
11
11
11
11
12
12
12
12
50
1
1
1
1
1
1
1
1
1
10
1
1
1
1
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
1
0.5
0.5
0.5
0.5
0.5
20
20
20
20
20
0
40
60
20
40
20
40
0
1.80
2.12
2.97
2.63
2.23
2.38
3.54
1.07
1.41
8.52
2.85
2.53
2.42
1.88
76.6
78.8
61.0
57.4
61.8
80.5
72.2
68.0
50.4
76.2
70.5
62.0
68.9
66.0
23.4
21.2
39.0
42.6
38.2
19.5
27.8
32.0
49.6
23.8
29.5
38.0
31.1
34.0
200
300
500
700
300
300
300
300
300
300
300
300
300
9
10
11
12
13
14
60
[a] Conditions: 5 µmol of pre-catalyst, Et2AlCl as co-catalyst, 30 mL of toluene (120 mL of toluene when determined at 10 atm). [b]
106 gmol–1 h. [c] Weight percent determined by GC analysis.
activities of complexes 5–8 showed that under the same tion temperature was also studied. The reaction was carried
conditions the activity order is 8 Ͼ 5 Ͼ 6 Ͼ 7. Unfortu- out at 0, 20, 40 and 60 °C, and the results showed that the
nately, it is difficult to establish a relationship between the highest catalytic activity was achieved at 40 °C. It seems
catalytic activities and the electronic and steric effects of the that in this example the lowering of ethylene solubility at
groups attached to the phosphorus and nickel atoms from higher temperature is not the main factor affecting the cata-
these results.
lytic activity of 11. It was also noted that prolonging the
It has been reported that the nickel complexes of N,N,P- reaction time led to a decrease of catalytic activity and an
tridentate ligands VI show high catalytic activity for ethyl- increase of the C6 fraction in the products. This increase of
ene oligomerisation in the presence of EtAlCl2.[8] We there- the proportion of C6 component may be due to co-oligo-
fore added a Ph2P group to the P-methyl of ligand 3 to merisation of C4 accumulated in the reaction vessel. The
construct the new N,N,P tridentate ligand 4. The nickel influence of pressure was similar to that with complex 5.
complexes of the ligand (11 and 12) show high catalytic Thus, an increase of ethylene pressure did not obviously
activity for ethylene oligomerisation in the presence of Et2-
AlCl (Table 2). In each case the reaction produced a mix-
ture of C4 and C6 species. The quantity of aluminium co-
catalyst affected the outcome of the reaction. For complex
11, enhancement of the Al/Ni molar ratio from 50:1 to
300:1 gave an increase in catalytic activity. With further
augmentation of the Al/Ni ratio the catalytic activity grad-
ually decreased (entries 1–5 in Table 2). The effect of reac-
Table 3. Ethylene oligomerisation with complexes 9, 10 and 13.[a]
Entry
Complex
Co-catalyst
Al/Co
Activity[b]
C4 [%][c]
C6 [%][c]
1
2
3
4
5
6
7
8
9
9
MAO
MAO
MAO
MAO
MAO
MAO
MAO
MAO
MAO
MMAO
MMAO
MMAO
MMAO
MMAO
MMAO
MMAO
MMAO
300
500
800
1000
1500
1800
2400
2400
2400
300
500
800
1000
1500
2000
2000
2000
very low
2.56
3.18
3.85
4.51
5.62
8.60
7.01
7.12
15.5
24.2
26.0
27.3
52.3
53.3
54.8
33.6
82.7
20.7
27.9
16.9
19.1
21.0
16.9
22.6
97.6
Ͼ99
Ͼ99
Ͼ99
Ͼ99
Ͼ99
Ͼ99
Ͼ99
17.3
79.3
72.1
83.1
80.9
79.0
83.1
77.4
2.4
9
9
9
9
9
10
13
9
9
10
11
12
13
14
15
16
17
9
9
9
9
9
10
13
[a] Conditions: 5 µmol of pre-catalyst, 20 °C, 30 mL of toluene, 1 atm of ethylene, 0.5 h. [b] 104 gmol–1 h. [c] Weight percent determined
by GC analysis.
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Co and Ni Complexes Bearing Pyrazolyliminophosphorane Ligands
FULL PAPER
and degassed prior to use. NMR spectra were recorded with a
Bruker av300 spectrometer at ambient temperature (300 MHz for
1H, 75.5 MHz for 13C and 121.5 MHz for 31P). The chemical shifts
of 1H and 13C NMR spectra are referenced to internal solvent reso-
nances; the 31P NMR spectra are referenced to external 85%
H3PO4. IR spectra were recorded with a Bruker VECTOR-22 spec-
trometer. Elemental analyses were performed by the Analytical
Centre of the University of Science and Technology of China. GC
analyses were performed with a Carlo Erba Strumentazione gas
chromatograph equipped with a flame ionisation detector and a
enhance the catalytic activity of 11 in unit pressure (en-
try 10 in Table 2). For complex 12, the highest activity was
observed at 20 °C and 1 atm of ethylene in the presence of
300 equiv. of Et2AlCl.
In addition, compared with the nickel complexes with
didentate ligands 5–8, complexes 11 and 12 exhibit higher
catalytic activity under similar reaction conditions.
The nature of the aluminium co-catalyst affects the cata-
lytic properties of the pre-catalysts greatly. As we mentioned
above, the cobalt complexes are inactive for ethylene oligo- 30 m (0.25 mm i.d., 0.25 µm film thickness) DM-1 silica capillary
column. High purity ethylene was purchased from Beijing Yanshan
Petrochemical Co. and used as received. Methylaluminoxane
(MAO, 1.46  in toluene) and modified methylaluminoxane
(MMAO, 1.93  in heptane) were purchased from Akzo Nobel
Corp. Et2AlCl was purchased from Fluka as a 1.90  solution in
hexane. 3,5-Dimethyl-1-(2Ј-azidophenyl)pyrazole and [NiCl2(dme)]
were prepared according to literature methods.[4f,14,18]
merisation with Et2AlCl as co-catalyst. However, they
showed good catalytic activities for ethylene oligomeris-
ation with MAO or MMAO as activator (Table 3). Com-
plexes 9, 10 and 13 showed similar catalytic activities when
MAO was used as co-catalyst (Al/Co = 2400) at 20 °C un-
der 1 atm of ethylene. The catalytic reaction yielded a mix-
ture of C4 and C6 species.
Preparations
When MMAO was used as co-catalyst, 13 revealed lower
activity than 9 and 10. However, each of complexes 9, 10 1-{o-(Ph3PN)C6H4}-3,5-Me2C3HN2 (2): A solution of 1 (2.09 g,
9.8 mmol) in CH2Cl2 (20 mL) was added to a stirred solution of
PPh3 (2.57 g, 9.8 mmol) in CH2Cl2 (10 mL) at room temperature
and the mixture was stirred overnight. Volatiles were removed in
vacuo and the residue was dissolved in diethyl ether. Filtration of
the solution and concentration of the filtrate afforded 2 as a yellow
and 13 exhibits higher activities than that with MAO as
activator under similar reaction conditions. We also tested
the effect of the Al/Co ratio for complex 9. Increase of the
MAO/Co or MMAO/Co ratio resulted in an enhancement
of catalytic activities (entries 1–7 and 10–15 in Table 3). An
important feature of the cobalt complex/MMAO systems
was the selectivity: in each case the reaction gave almost
single C4 species.
1
powder (3.95 g, 90.2%), m.p. 126–127 °C. H NMR (CDCl3): δ =
2.02 (s, 3 H, CH3), 2.25 (s, 3 H, CH3), 5.89 (s, 1 H, CH), 6.42 (d,
J = 7.8 Hz, 1 H, C6H4), 6.58 (t, J = 7.5 Hz, 1 H, C6H4), 6.81 (dt,
J = 7.5, 8.1 Hz, 1 H, C6H4), 7.14–7.20 (m, 1 H, C6H4), 7.25–7.31
(m, 6 H, Ph), 7.35–7.39 (m, 3 H, Ph), 7.47–7.54 (m, 6 H, Ph) ppm.
13C NMR (CDCl3): δ = 11.8, 13.9, 104.0, 117.1, 122.1 (d, J =
9.4 Hz), 128.5 (d, J = 12.1 Hz), 128.7, 130.5, 131.6 (d, J = 2.7 Hz),
131.8, 132.6 (d, J = 9.8 Hz), 134.5, 134.8, 141.7, 147.5 ppm. 31P
Conclusions
NMR (CDCl ): δ = –3.56 ppm. IR: ν = 3049 cm–1 w, 3017 vw,
We have synthesised and characterised a set of novel N,N
and N,N,P chelating ligands and their nickel and cobalt
complexes. Upon activation with Et2AlCl, the nickel com-
plexes reveal high catalytic activity for the dimerisation and
trimerisation of ethylene under the optimal conditions,
whereas the cobalt complexes are inactive. When activated
with MAO or MMAO the cobalt complexes exhibit high
catalytic activities. It was also observed that the catalytic
activity of complex 9 increases with an increase of the Al/
Co ratio. When activated with MMAO, the cobalt com-
plexes show high selectivity, forming almost single C4 spe-
cies. Investigation of the action of the ligands revealed that
the nickel complexes with the tridentate ligand have a
higher catalytic activity than those with didentate ligands
when activated with Et2AlCl. However, the cobalt com-
plexes with tridentate ligands exhibit lower activity than
those with didentate ligands when activated with MMAO.
When MAO was used as activator, the cobalt complexes
with either tridentate or didentate ligands show similar
catalytic activity.
˜
3
2960 vw, 2925 w, 1591 m, 1548 m, 1496 vs, 1472 s, 1460 s, 1438 s,
1378 m, 1366 m, 1343 vs, 1314 m, 1288 m, 1164 w, 1137 w, 1109 vs,
1054 m, 1033 m, 1020 m, 997 m, 930 w, 780 m, 768 m, 764 s, 718 vs,
694 s, 657 w, 648 w. C29H26N3P (447.511): calcd. C 77.83, H 5.85,
N 9.39; found C 77.50, H 5.87, N 9.49.
1-{o-(Ph2MePN)C6H4}-3,5-Me2C3HN2 (3): This compound was
prepared using a similar method to that for 2. Reaction of Ph2PMe
(1.67 g, 8.4 mmol) with 1 (1.78 g, 8.4 mmol) in CH2Cl2 (30 mL)
gave orange crystals of 3 (2.74 g, 84.5%), m.p. 86–87 °C. 1H NMR
(CDCl3): δ = 1.96 (d, J = 12.6 Hz, 3 H, CH3), 2.21 (s, 3 H, CH3),
2.32 (s, 3 H, CH3), 5.93 (s, 1 H, CH), 6.54 (d, J = 8.1 Hz, 1 H,
C6H4), 6.71 (t, J = 7.2 Hz, 1 H, C6H4), 6.95–7.01 (m, 1 H, C6H4),
7.24–7.27 (m, 1 H, C6H4), 7.32–7.49 (m, 6 H, Ph), 7.57–7.63 (m, 4
H, Ph) ppm. 13C NMR (CDCl3): δ = 11.9, 13.8, 14.0 (d, J =
62.4 Hz), 104.2, 117.4, 123.0 (d, J = 10.9 Hz), 128.6 (d, J = 12 Hz),
128.8 (d, J = 3.8 Hz), 131.2 (d, J = 9.8 Hz), 131.5 (d, J = 2.9 Hz),
134.7, 135.0, 141.7, 147.6, 147.9 ppm. 31P NMR (CDCl3): δ =
–2.14 ppm. IR: ν = 3051 cm–1 m, 3039 m, 2951 w, 2915 m, 1591 s,
˜
1549 m, 1499 vs, 1427 s, 1436 s, 1417 m, 1358 vs, 1316 m, 1289 m,
1276 m, 1160 w, 1116 s, 1055 m, 1033 m, 1022 m, 998 w, 927 vw,
879 m, 869 m, 768 m, 753 s, 741 s, 732 s, 711 m, 692 s, 648 m.
C24H24N3P (385.441): calcd. C 74.79, H 6.27, N 10.90; found C
74.69, H 6.29, N 11.16.
Experimental Section
1-[o-{Ph2PCH2P(Ph)2N}C6H4]-3,5-Me2C3HN2 (4): A solution of 1
(3.33 g, 15.6 mmol) in CH2Cl2 (20 mL) was added to a stirred solu-
tion of Ph2PCH2PPh2 (6.01 g, 15.6 mmol) in CH2Cl2 (10 mL) at
0 °C and the mixture was stirred overnight at room temperature.
Volatiles were removed in vacuo and the residue was dissolved in
General Procedure: All air- or moisture-sensitive manipulations
were performed under dry N2 using standard Schlenk and vacuum-
line techniques. Solvents were distilled under N2 over sodium/
benzophenone (toluene, n-hexane, thf and Et2O) or CaH2 (CH2Cl2)
Eur. J. Inorg. Chem. 2006, 4895–4902
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
4899

C. Zhang, W.-H. Sun, Z.-X. Wang
FULL PAPER
diethyl ether (20 mL). Filtration of the solution and concentration
concentrated to about 2 mL. Toluene was added to give
of the filtrate produced 4 as a yellow powder (7.36 g, 82.7%), m.p.
8·CH2Cl2·0.3THF as a blue powder (0.414 g, 80.2%), m.p. 117–
1
130–131 °C. H NMR (CDCl3): δ = 2.13 (s, 3 H, CH3), 2.25 (s, 3 118 °C. IR (KBr): ν = 3052 cm–1 w, 2986 w, 2915 w, 1594 m,
˜
H, CH3), 3.07 (d, J = 12.5 Hz, 2 H, CH2), 5.81 (s, 1 H, CH), 6.38
1556 m, 1499 s, 1487 m, 1450 m, 1437 s, 1390 m, 1374 m, 1302 m,
(d, J = 8.0 Hz, 1 H, C6H4), 6.64 (t, J = 7.6 Hz, 1 H, C6H4), 6.80– 1274 s, 1238 m, 1150 w, 1114 vs, 1067 m, 1010 s, 998 s, 897 s, 866 w,
6.85 (m, 1 H, C6H4), 7.11–7.24 (m, 15 H, Ph, C6H4), 7.32 (d, J = 801 m, 786 m, 780 m, 749 vs, 729 s, 695 s, 668 w, 616 w.
7.1 Hz, 2 H, Ph), 7.47–7.53 (m, 4 H, Ph) ppm. 13C NMR (CDCl3):
δ = 12.0, 13.9, 29.6 (dd, J = 61.8, 70.8 Hz), 104.2, 117.4, 123.3 (d,
J = 10.3 Hz), 128.4, 128.49, 128.54, 128.65, 128.75, 131.5, 131. 9
(d, J = 9.1 Hz), 132.7, 133.0, 134.6, 134.9, 142.0, 147.5 ppm. 31P
NMR (CDCl3): δ = –1.98 (d, J = 51.9 Hz), –31.42 (d, J = 52.6 Hz)
C24H24Cl2N3NiP·CH2Cl2·0.3THF (621.60): calcd. C 50.62, H 4.61,
N 6.76, found C 50.82, H 4.51, N 7.10.
[{1-[o-(Ph3PN)C6H4]-3,5-Me2C3HN2}CoCl2] (9): A solution of li-
gand 2 (0.432 g, 0.96 mmol) in thf (10 mL) was added to a stirred
suspension of CoCl2 (0.125 g, 0.96 mmol) in thf (10 mL) at room
temperature and the mixture was allowed to stir overnight. The
solvent was then removed under vacuum and the residue was dis-
solved in CH2Cl2. The solution was filtered and the filtrate was
concentrated to about 2 mL. Hexane was added to give 9 as a blue
ppm. IR: ν = 3054 cm–1 m, 2923 m, 1595 m, 1547 m, 1498 vs,
˜
1468 s, 1433 s, 1365 vs, 1357, 1309 w, 1289 w, 1182 vw, 1155 vw,
1118 m, 1060 w, 1022 m, 998 w, 930 vw, 798 w, 778 m, 765 w,
735 vs, 694 s, 643 w. C36H33N3P2 (569.615): calcd. C 75.91, H 5.84,
N 7.38; found C 75.79, H 5.91, N 7.68.
powder (0.535 g, 96.4%), m.p. 268–269 °C. IR (KBr):
ν =
˜
[{1-[o-(Ph3PN)C6H4]-3,5-Me2C3HN2}NiBr2] (5): A solution of 2
(0.552 g, 1.23 mmol) in thf (10 mL) was added to a suspension of
3057 cm–1 w, 2958 vw, 2922 w, 2853 vw, 1590 m, 1549 m, 1496 s,
1484 s, 1438 vs, 1389 w, 1366 m, 1313 w, 1278 m, 1260 vs, 1232 s,
NiBr2 (0.270 g, 1.23 mmol) in thf (10 mL) and the mixture was 1188 w, 1158 vw, 1138 w, 1125 s, 1108 vs, 1048 m, 1027 w, 1006 m,
stirred overnight at room temperature. The solvent was then re-
moved under vacuum and the residue was dissolved in CH2Cl2.
The solution was filtered and the filtrate was concentrated to about
3 mL. Toluene was added to the solution to give 5 as a blue powder
992 s, 807 s, 781 s, 753 s, 742 m, 721 s, 694 s, 666 m, 645 w, 621 m.
C29H26Cl2CoN3P (577.35): calcd. C 60.33, H 4.54, N 7.28; found
C 60.34, H 4.53, N 7.55.
[{1-[o-(Ph2MePN)C6H4]-3,5-Me2C3HN2}CoCl2] (10): A solution of
3 (0.326 g, 0.85 mmol) in thf (10 mL) was added to a stirred suspen-
sion of CoCl2 (0.110 g, 0.85 mmol) in thf (10 mL) at room tempera-
ture and the mixture was allowed to stir overnight. The solvent
was then removed under vacuum and the residue was dissolved in
CH2Cl2. The solution was filtered and the filtrate was concentrated
to about 2 mL. Toluene was added to produce blue crystals of
(0.693 g, 93.6%), m.p. 311–312 °C. IR (KBr): ν = 3055 cm–1 w,
˜
3047 w, 2958 vw, 2922 w, 1590 w, 1549 m, 1497 m, 1483 m, 1438 vs,
1366 m, 1279 m, 1263 vs, 1232 m, 1187 w, 1125 m, 1107 vs, 1058 w,
1047 m, 1005 m, 993 s, 811 s, 783 m, 753 s, 741 m, 721 s, 694 s,
667 w, 622 w. C29H26Br2N3NiP (666.01): calcd. C 52.29, H 3.93, N
6.31; found C 52.34, H 3.88, N 6.48.
[{1-[o-(Ph3PN)C6H4]-3,5-Me2C3HN2}NiCl2] (6): A solution of 2
(0.407 g, 0.91 mmol) in thf (10 mL) was added to a stirred suspen-
sion of [NiCl2(dme)] (0.200 g, 0.91 mmol) in thf (10 mL) at room
temperature and the mixture was stirred overnight at room tem-
perature. The volatiles were removed under vacuum and the residue
was dissolved in CH2Cl2 (10 mL). The solution was filtered and the
filtrate was concentrated to about 2 mL. Hexane was added to the
solution to give 6 as a blue powder (0.477 g, 90.8%), m.p. 275–
10·1.5C7H8 (0.404 g, 72.7%), m.p. 125–126 °C. IR (KBr): ν =
˜
3053 cm–1 w, 2985 w, 2914 w, 1592 m, 1552 m, 1498 s, 1484 m,
1437 s, 1423 m, 1388 w, 1371 m, 1302 m, 1272 s, 1236 m, 1161 w,
1144 w, 1113 s, 1064 m, 998 s, 949 w, 898 s, 798 w, 777 m, 749 s,
728 m, 695 m, 666 w, 614 w. C24H24Cl2CoN3P·1.5C7H8 (653.49):
calcd. C 63.41, H 5.55, N 6.43; found C 63.24, H 5.47, N 6.52.
[{1-[o-(Ph2PCH2PPh2N)C6H4]-3,5-Me2C3HN2}NiBr2] (11): A solu-
tion of 4 (0.524 g, 0.92 mmol) in thf (10 mL) was added to a sus-
pension of NiBr2 (0.201 g, 0.92 mmol) in thf (5 mL) at room tem-
perature with stirring and the mixture was allowed to stir for 4 h.
The solvent was then removed under vacuum and the residue was
dissolved in CH2Cl2 (10 mL). The solution was filtered and the
filtrate was concentrated to about 4 mL. Hexane (10 mL) was
added to produce purple microcrystals of 11 (0.693 g, 95.6%), m.p.
225–226 °C. An analytically pure sample was obtained by
276 °C. IR (KBr): ν = 3065 cm–1 w, 2970 vw, 2926 vw, 1591 m,
˜
1549 m, 1497 s, 1487 s, 1437 vs, 1389 w, 1368 m, 1283 m, 1263 s,
1233 m, 1188 w, 1140 w, 1110 s, 1048 m, 1029 w, 994 m, 812 s,
783 m, 756 s, 744 m, 723 s, 695 s, 678 w, 612 w. C29H26Cl2N3NiP
(577.11): calcd. C 60.35, H 4.75, N 7.28; found C 60.39, H 4.64, N
7.29.
[{1-[o-(Ph2MePN)C6H4]-3,5-Me2C3HN2}NiBr2] (7): A solution of 3
(0.278 g, 0.72 mmol) in thf (10 mL) was added to a stirred suspen-
sion of NiBr2 (0.158 g, 0.72 mmol) in thf (10 mL) at room tempera-
ture and the mixture was allowed to stir overnight. The solvent
was then removed under vacuum and the residue was dissolved in
CH2Cl2. The solution was filtered and the filtrate was concentrated
to about 2 mL. Toluene was added to yield blue crystals of
recrystallisation from a mixture of dmf and benzene. IR (KBr): ν
˜
= 3052 cm–1 m, 3016 w, 2987 w, 2960 vw, 2816 w, 1590 m, 1553 m,
1499 vs, 1484 s, 1454 s, 1436 vs, 1389 m, 1366 m, 1298 s, 1241 m,
1190 w, 1160 m, 1114 vs, 1047 m, 997 s, 804 s, 782 vs, 741 vs, 725 s,
691 vs, 642 w, 615 w. C36H33Br2N3NiP2·THF·C6H6 (938.33): calcd.
C 57.54, H 4.93, N 5.96; found C 57.24, H 4.82, N 5.83.
7·CH2Cl2 (0.427 g, 86.1%), m.p. 239–240 °C. IR (KBr): ν =
˜
[{1-[o-(Ph2PCH2PPh2N)C6H4]-3,5-Me2C3HN2}NiCl2] (12): A solu-
tion of 4 (0.337 g, 0.59 mmol) in thf (10 mL) was added to a stirred
suspension of [NiCl2(dme)] (0.130 g, 0.59 mmol) in thf (10 mL) and
the mixture was stirred overnight at room temperature. The vola-
tiles were then removed under vacuum and the residue was dis-
solved in CH2Cl2. The solution was filtered and the filtrate was
concentrated to about 2 mL. Toluene was added to produce yellow
3056 cm–1 w, 2987 w, 2916 w, 1593 m, 1550 m, 1499 s, 1453 m,
1437 s, 1419 m, 1389 w, 1373 w, 1298 m, 1272 s, 1236 m, 1160 w,
1117 vs, 1061 w, 1047 w, 1010 s, 996 s, 894 s, 799 w, 781 m, 743 vs,
716 w, 693 s, 667 s, 615 w. C24H24Br2N3NiP·CH2Cl2 (688.88): calcd.
C 43.59, H 3.80, N 6.10; found C 43.72, H 3.82, N 6.17.
[{1-[o-(Ph2MePN)C6H4]-3,5-Me2C3HN2}NiCl2] (8): A solution of 3
(0.321 g, 0.83 mmol) in thf (10 mL) was added to a stirred suspen-
sion of [NiCl2(dme)] (0.183 g, 0.83 mmol) in thf (10 mL) at room
temperature and the mixture was allowed to stir overnight. The
volatiles were then removed under vacuum and the residue was
dissolved in CH2Cl2. The solution was filtered and the filtrate was
crystals of 12·THF (0.379 g, 83.3%), m.p. 180–181 °C. IR (KBr): ν
˜
= 3055 cm–1 w, 3028 w, 2963 w, 2904 w, 1590 m, 1556 m, 1496 s,
1486 s, 1447 m, 1435 vs, 1371 m, 1291 s, 1241 m, 1142 m, 1112 s,
1058 m, 1028 w, 996 s, 802 m, 782 s, 770 s, 739 s, 720 s, 693 s, 616 w.
C36H33Cl2N3NiP2·THF (771.32): calcd. C 62.29, H 5.36, N 5.45;
4900
www.eurjic.org
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2006, 4895–4902

Co and Ni Complexes Bearing Pyrazolyliminophosphorane Ligands
FULL PAPER
Table 4. Details of the X-ray structure determinations of complexes 5, 9 and 12.
5
9
12·C7H8
Empirical formula
Formula mass
C29H26Br2N3NiP
666.03
C29H26Cl2CoN3P
577.33
C43H41Cl2N3NiP2
791.34
Crystal system
Space group
orthorhombic
Pbca
orthorhombic
Pbca
monoclinic
P21/c
a [Å]
b [Å]
c [Å]
α [°]
18.168(4)
16.691(4)
18.302(4)
90
16.597(2)
18.007(2)
18.198(2)
90
14.793(2)
13.929(2)
20.250(3)
90
β [°]
90
90
5550(2)
8
90
90
109.793(3)
90
3926.2(11)
4
γ [°]
V [Å3]
5438.5(12)
8
1.410
Z
Dcalcd. [gcm–3]
1.594
1.339
F(000)
2672
3.660
2376
0.910
1648
0.746
µ [mm–1]
θ range for data collection [°]
No. of reflns. collected
No. of independent reflns. (Rint
2.00 to 26.40
29235
5662 (Rint = 0.0652)
2.01 to 27.19
29912
5876 (Rint = 0.0681)
5876 / 0 / 327
1.050
R1 = 0.0415
wR2 = 0.0806
R1 = 0.0899
wR2 = 0.0997
0.364 and –0.384
1.46 to 25.95
20646
7598 (Rint = 0.0569)
7598 / 0 / 463
1.013
R1 = 0.0484,
wR2 = 0.1092
R1 = 0.0960,
wR2 = 0.1353
0.778 and –0.431
)
No. of data / restraints / parameters 5662 / 0 / 327
Goodness of fit on F2
1.125
Final R indices[a] [I Ͼ 2σ(I)]
R1 = 0.0615
wR2 = 0.1973
R1 = 0.0964
wR2 = 0.2185
1.082 and –0.803
R indices (all data)
Largest diff. peak and hole [eÅ–3]
2
2 2
[a] R1 = Σ||Fo| – |Fc||/Σ|Fo|; wR2 = [Σw(Fo – Fc ) /Σw(Fo4)]1/2
.
found C 62.60, H 5.16, N 5.35. Single crystals suitable for X-ray
diffraction analysis were obtained by recrystallisation of 12 from
toluene (thf was removed from 12·THF under vacuum prior to
recrystallisation).
with ethylene. Toluene (30 mL) was added to the tube and then
the appropriate co-catalyst solution was added with a syringe. The
reaction mixture was vigorously stirred at the given temperature
under 1 atm of ethylene. After the desired period of time (30 or
60 min), the reaction was terminated by adding 10% HCl solution
(30 mL). About 1 mL of the organic layer was dried with anhy-
drous Na2SO4 for GC analysis. Ethanol (100 mL) was added to the
remaining solution; no polymer was observed.
[{1-[o-(Ph2PCH2PPh2N)C6H4]-3,5-Me2C3HN2}CoCl2] (13): A solu-
tion of 4 (0.482 g, 0.85 mmol) in thf (10 mL) was added to a sus-
pension of CoCl2 (0.110 g, 0.85 mmol) in thf (10 mL) at room tem-
perature with stirring. The volatiles were then removed under vac-
uum and the residue was dissolved in CH2Cl2. The solution was
filtered and the filtrate was concentrated to about 2 mL. Toluene
was added to produce blue crystals of 13·0.75C7H8 (0.567 g,
The oligomerisation with 10 atm of ethylene was carried out in a
stainless-steel autoclave (250 mL capacity) equipped with a gas bal-
last through a solenoid valve for continuous feeding of ethylene at
constant pressure. Toluene (120 mL) containing the pre-catalyst
was transferred into the fully dried reactor under N2 atmosphere.
The required amount of co-catalyst was injected into the reactor
with a syringe. Once the desired temperature had been reached the
reactor was pressurised to 10 atm. After stirring for 30 min, the
reaction was quenched and worked-up using the same procedure
as described above for the reaction at 1 atm.
86.8%), m.p. 129–130 °C. IR (KBr): ν = 3052 cm–1 m, 3021 m,
˜
2950 m, 2924 m, 2902 m, 1590 s, 1572 w, 1556 s, 1495 s, 1481 s,
1467 s, 1435 vs, 1372 s, 1361 s, 1301 s, 1267 vs, 1239 s, 1189 w,
1158 w, 1139 s, 1111 vs, 1057 s, 1044 s, 1028 m, 991 vs, 938 w, 922 w,
825 w, 800 s, 782 vs, 769 vs, 739 vs, 717 vs, 694 vs, 662 s, 638 m,
616 m. C36H33Cl2CoN3P2·0.75C7H8 (768.56): calcd. C 64.46, H
5.11, N 5.46; found C 64.24, H 5.16, N 5.41.
X-ray Crystallography: Crystals were mounted in Lindemann capil-
laries under N2. Diffraction data were collected on a Siemens CCD
area detector at 294(2) K with graphite-monochromated Mo-Kα ra-
diation (λ = 0.71073 Å). A semi-empirical absorption correction
was applied to the data. The structures were solved by direct meth-
ods using SHELXS-97[19] and refined against F2 by full-matrix le-
ast-squares using SHELXL-97.[20] Crystal data and experimental
details of the structure determinations are listed in Table 4.
Acknowledgments
This work was supported by the National Natural Science Founda-
tion of China (grant no. 20272056). Z. X. W. thanks Professors H.-
B. Song and H.-G. Wang for the single-crystal X-ray structure de-
terminations.
CCDC-606680 (for 5), -606681 (for 9) and -617850 (for 12) contain
the supplementary crystallographic data for this paper. These data
can be obtained free of charge from The Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
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ation with 1 atm of ethylene was carried out in a Schlenk tube.
Thus, the pre-catalyst (5 µmol) was added to a dried Schlenk tube
and then the tube was back-filled three times with N2 and twice
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© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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4901

C. Zhang, W.-H. Sun, Z.-X. Wang
FULL PAPER
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Published Online: October 18, 2006
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